Handle Julia 1.14's syntax-versioned module expression in @testsetup

[PingoLee]

Fixes #245.

On Julia 1.14 the module expression a macro receives can carry a leading syntax version,
Expr(:module, v"1.14.0", true, :Name, body) (JuliaLang/julia#60018), and @testsetup's
positional _, name, code = mod.args then binds name = true.

• src/macros.jl: read name and body from the end of mod.args, which is correct for both the
  3-argument and the 4-argument form.
• src/ReTestItems.jl: set the evaluated setup module's body with args[end] instead of
  args[3]. That isn't broken today, because the quoted :(module … end) is parsed under this
  package's own julia = "1.8" syntax version, but it has the same positional assumption and would
  silently overwrite the module name once that compat moves to 1.14.
• test/macros.jl: a regression test that builds the 4-argument form directly, so it runs on every
  CI version rather than only on 1.14+.
• Version bump to 1.35.4.

Tested:

• test/macros.jl: the new test errors with "@testsetup module expects a valid module name"
  without the src/ change and passes with it, on 1.12.7 and 1.14.0-DEV.3477.
• Full Pkg.test(): 2039 pass / 3 broken on 1.12.7, and 1983 pass / 3 broken on
  1.14.0-DEV.3477 (the JUnit reference tests are skipped on prereleases, as runtests.jl intends).
  Under 1.14, Pkg.test's sandbox parses with the 1.14 syntax version, so unpatched test/macros.jl
  cannot even be lowered there.
• Downstream: a package whose suite uses @testsetup collects and runs on 1.14.0-DEV.3477 with
  this branch. Without it, collection fails at the first @testsetup.

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